Conventionally, it is known that a fuel pump intakes fuel into a rotor housing chamber and then discharges the fuel. A fuel pump disclosed in JP 2009-250087 A includes a rotor that rotates, a pump housing, a cylindrical portion, and an outer circumferential side housing. The pump housing interposes the rotor from both side in the axial direction, and defines a rotor housing chamber that rotatably houses the rotor. The cylindrical portion is formed in a cylindrical shape that surrounds the pump housing from the outer circumferential side. The outer circumferential side housing includes a narrowing portion that has a diameter which narrows down compared to the cylindrical portion.
Here, a groove is formed in the outer circumferential side housing. The groove makes a round along the circumferential direction of this outer circumferential side housing. Then, when manufacturing the fuel pump, by folding the narrowing portion from the groove, the narrowing portion is joined with a joining portion of the pump housing. In other words, since the thickness of the outer circumferential side housing becomes thinner at the narrowing portion, the narrowing portion and the joining portion are joined together without strongly pressing the narrowing portion into the joining portion, and making it difficult for springback to occur. As a result, distortions in the pump housing are suppressed.